1. Field of the Invention
The present invention relates generally to ratchet wrenches, and relates more specifically to a self-contained ratcheting mechanism with a reversing knob and dual pawls.
2. Description of the Prior Art
Dual-pawl reversible ratchet wrenches are well known in the art. Typically, such ratchet wrenches include a self-contained ratcheting mechanism having a reversing knob securely retained to a ratcheting assembly. The reversing knob is coupled to pivotally mounted left and right pawls with teeth on their outer ends. The pawls are mounted to engage ratchet teeth formed on the inner surface of a bore in the ratchet head into which the self-contained ratcheting mechanism is received. Rotational movement of the reversing knob to one position urges one end of one pawl and the opposite end of the other pawl into engagement with the teeth of the ratchet head. The purpose of these pawls, and pawls in general, being to prevent rotation in one direction while allowing rotation in the opposite direction. Upon actuation of the reversing knob to the opposite position, the pawls are pivoted causing the engaged teeth on the pawls to become disengaged and the respective other ends thereof to be urged against the teeth of the ratchet head.
A conventional type dual-pawl ratchet wrench with a self-contained ratcheting mechanism is described in U.S. Pat. No. 4,765,449 to Peters. The pawls in such a construction move in tandem as they pivot. They are generally elongated and their longitudinal axes are supposed to be maintained substantially parallel. The construction of dual-pawl ratchets is such that, under high loading and/or wear, one pawl could oppose the other, causing the mechanism to jam. In the jammed condition, illustrated in prior art FIG. 1, the pawls 1, 2 move to a pigeon-toe-like position with their longitudinal axes intersecting so that the same ends of both pawls are engaged, thus opposing rotation in the opposite directions, and the ratchet may not be operated in either direction. It should be understood that the jammed condition shown in FIG. 1 cannot occur in single-pawl ratchet assemblies.
In conventional dual-pawl ratchets, a selector knob cooperates with plungers and springs for operation of the ratchet between the forward and reverse directions, all in a well known manner. Occasionally, a reversing movement of the selector knob reverses only one of the pawls, resulting in the pigeon-toe position described above, causing the ratchet to become jammed or locked-up, as described below.
Pawl jamming (pigeon-toeing) of dual-pawl ratchets may occur under a number of differing situations and is generally facilitated by heavy loading, component distortion or component wear. Jamming generally occurs when one pawl becomes disengaged in response to a reversing movement of the selector knob, while the other pawl--usually a pawl under an applied or residual loading force to the ratchet head--remains engaged. Thus, the disengaged pawl moves into a reversed or opposing condition relative to the other pawl such that the pawls are in the pigeon-toe position and the ratchet mechanism is said to be jammed.
It is a well known phenomenon that the unique geometry and relative positions of the pawls of dual-pawl assemblies causes one pawl to bear a force greater than the opposite pawl during a loading situation. As a result, if the ratchet tool user attempts to manually turn the selector knob, in an effort to reverse the dual-pawl ratchet assembly, while continuing to apply a loading force on the ratchet head, the pivoting force on the selector knob may not be great enough to overcome the loading force on the more heavily loaded pawl. Thus, only one pawl will reverse, resulting in the jammed condition.
The same jamming condition can also result during a sudden acceleration of the ratchet, as during the sudden release which may occur during loosening of a stuck fastener. This acceleration generates an inertial force of sufficient magnitude to cause the selector knob assembly to self-rotate. This could cause the engaged pawl, i.e., the pawl imparting the bulk of the loosening load, to remain engaged while the opposite pawl pivots to its opposite position in pigeon-toe relation to the engaged pawl, causing the ratchet to become jammed.
Air driven ratchet tools impart a loading torque in a given direction (tightening or loosening directions) by rapidly oscillating between a loading and ratcheting conditions during a torquing operation. The vibration associated with this oscillation could result in a reversal of only one pawl, resulting in the jammed condition.
It is further possible that a lockup (pigeon-toeing) of the pawls could occur during ratcheting (non-load mode), possibly due to the high speed oscillation phenomenon of the pawls as they ride over the ratchet head teeth, causing one (or both) of the pawls to flip to an opposing condition, aided by its rotational inertia, and jamming the ratchet.
Thus, there is a need to provide a ratchet wrench with a mechanism that would prevent the pawls from jamming in this manner but which is easy and economical to assemble and manufacture.